Part A Introduction:
All waves in nature travel at some speed. During a thunderstorm, the difference between seeing
the flash of lightening and hearing it, in seconds, can be used to approximate how far away the
lightening occurred (count the number of seconds between flash and thunder, divide by 3 to get
distance away in km, divide by 5 to get miles). This is because sound waves travel at a much
slower speed than do light waves emitted from lightening. The light waves tell us when to start
counting and our knowledge of the speed of sound in air tells us the distant to the source.
A water wave travels at a different, but fixed speed. If you sit in one place in a boat after the
neighborhood speedboat bully has zoomed by, you will bob up and down so many times in a
minute, depending on the distance between successive waves. How many times you bob per
second defines the wave’s frequency.